Border Collie Aggression

I have a female border collie that has just turned two years old, and a male wheaten terrier that is 9 years old. For the past few days my border collie has been biting and acting very aggressive to my terrier. It all started few weeks ago when I was playing with my border collie and stopped for a second to pet my wheaten terrier, who had just walked up to my side. She came over to him and nipped his face , at which time I gave her a command to lie down ; tried to physically separate them ( A bad move on my part.) a fur ball ensued, during which I was bitten as I pulled her mouth away from his throat. The good news is they are both in good health and none of the bites broke there skin. I have used every discipline technique that I can think of (short of hitting), and have consulted a local Border collie trainer with no change. The other day I watched the wheaten terrier’s foot collapse on him when he was walking, so he may have had a small seizure, but I am not sure if this would cause my border collie to have a change in attitude towards him.

What did the trainer you consulted offer for advice and/or training? That would help people give a little more advice....
Obviously, I'm not a professional trainer or behaviorist (and I'm not there to see what actually happened), but it could be possible that if he was the "higher" ranking dog and she senses that he's ill or is getting weak due to age, she might try and get in there to flip roles between the two of them.
A sudden change in behavior would also make me wonder if she was medically sound though? I'd take her to the vet and make sure. It doesn't sound like that's the case, but many dogs have had "attitude" changes due to an underlying medical condition.
I would caution discipline with behaviors like this as well. (my opinion) Sometimes using adversaries or punishment to "correct" a dog from acting aggressive/fearful/rude (anything) can actually instill fear in the dog and cause a bigger problem leading to fear aggression.
That being said, my dog has a tendency to get snotty with other dogs when I am giving them attention. Not to this degree, but she will separate us and bully her way in for attention. What I would do is have both dogs sit near you and while your giving attention to your terrier, give the other dog praise and/or treats for acting properly around him. I would do this quite a few times a day (just for a couple of minutes) for a couple of weeks to see if anything improves. I would also start watching your border collie for signs that she might be getting ready to do something and stop it there. Have her do something else more productive. Watch for intense "eye", tightened mouth, ears back, ears forward and "hard" with stiff, slowly moving tail, dilated pupils, big round eyes, there are lots of signs, try and track down a copy of Turid Rugaas' book on calming signals and the DVD. They are a very educational pair to have in your collection.
Also, there are many things you can to to avoid getting into the middle of a dog fight. Clanging something metal, making a really loud noise, dropping something on the floor (phone book), a shake can (pop can filled with pennies), a spray bottle to squirt them with (if outside, garden hose), tossing a blanket or towel over each dog etc.
Oh, is she spayed?

Just my thoughts hopefully more people will chime in and give you a lot of resources....

I would take the wheaten terrier to the vet too to check his health, because I second what Daisy is saying above. Since I started volunteering at the pound, I have witnessed several situations in which healthy, previously dog-friendly and sociable dogs turned on dogs they perceived to be weak: for example, a dog with a large scar on its back, a dog who is limping, that sort of thing. I have no background to be able to speculate why this is, but in talking with actual employees at the animal control center about the incidents I witnessed (one of which was severe and caused me to RUN inside and scream help help so an employee could get a smaller dog away from a large GSD and bring him into SURGERY to save his life), they weren't surprised. So yeah, take not only the BC to the vet, but also the wheaten terrier too, to see if your BC is maybe noticing something about him you haven't. And I second what Daisy said about spay status also; I've personally experienced *severe* personality changes related to heat cycles myself! And I've read about that a lot on here too.

The trainer in my area told me to never get between a dog fight and to use a deep voice to break the dog’s attention. He also told me not to separate them and to try to give both equal attention. On the medical question my border collie (Ann) is very healthy and has always displayed a playful passive attitude. The wheaten terrier (Patrick) on the other hand is in bad health. He has an untreatable heart condition and has trouble breathing, but is always friendly. On the morning before the fight Ann grabbed onto an electrified fence with her mouth. She was quite nervous after the shock but went on to play fetch, and seemed back to her regular self after an hour or so.

On the morning before the fight Ann grabbed onto an electrified fence with her mouth. She was quite nervous after the shock but went on to play fetch, and seemed back to her regular self after an hour or so.

I'm no professional, but I think that's a real big coincidence if it is one... Especially if Patrick has been unhealthy for years and she has always ignored it. Anyway, three questions people will probably need answered before giving any further speculation are:

#1 (I doubt this now, but just in case) Has Patrick experienced any major change in health lately (just preceding the electrified fence bite/ first fight day)?#2 How long ago was the electrified fence bite/ first fight day?#3 Since then, has Ann beenexhibiting any other signs of nervousness since her accident (such as, ears back more often, hiding more often, tail between legs more often, looking away more often (or half moon eye), panting, low barely audible growling, freezing in place, stiffening, mild piloerection, etc.)?

You may want to watch closely for #3 and see if there is anything you've missed. Here are some links someone sent me here a while back that can really help you notice nervousness in your dog, before she actually gets aggressive: http://www.squidoo.com/readyerdog and http://www.familypaw.../communication/. If you do happen to catch her doing some of this in response to the terrier, you may want to look at him and see what he's doing. Your BC may not be feeling quite right and thus things he has always done now make *her* nervous. When my BC feels poorly (i.e., the first week after I give her her pre-heartworm treatment drugs), she does not tolerate other dogs invading her space well (not a full-blown fight like you describe, but she will snap, so when she feels poorly I keep her from encountering other dogs). Even though when she feels good, she is a doll.

Still, you should probably get your BC checked out by a vet and/or a veterinary behaviorist if the vet doesn't see anything wrong.